1. Having a quarantine tank on hand is a very good practice to use if you frequently buy new fish. The quarantine tank will weed out any sick fish that could possible get into your aquarium and cause harm to the other inhabitants.
2. After establishing your aquarium, pick fish that will add well to the current water conditions in your aquarium. Also be sure to check their temperament and other needs to be sure that they will make the transition in your aquarium smoothly.
3. Always use a new or clean bucket when going through the acclimation or water changing process. A bucket that has been used to hold bleach or other chemicals can be very harmful for the fish in your aquarium.